Liquid crystal display with pixel electrode having aperture containing additional electrode

ABSTRACT

An LCD (Liquid Crystal Display) including two substrates sandwiching an LC layer therebetween, and causing a plurality of different kinds of regions to coexist in the LC layer is disclosed. An electrode formed with an aperture is provided on at least one of the substrates. A second electrode is also provided on the same substrate as the above electrode in alignment with the electrode. A voltage higher than a voltage to be applied between the electrode with the aperture and a counter electrode facing it is applied between the second electrode and the counter electrode, thereby controlling the rising direction of LC molecules. The LCD is easy to produce and achieves a great viewing angle. In addition, the LC contains a polymer in order to fix the rising directions of the LC molecules.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/841,103, filedApr. 30, 1997 U.S. Pat. No. 5,963,290.

BACKGROUND OF THE INVENTION

The present invention relates to an LCD (Liquid Crystal Display) fordisplaying images including texts and graphics and, more particularly,to a method of producing and driving an LCD which is easy to produce andhas a desirable viewing angle characteristic.

In a TN (Twisted Nematic) type LCD extensively used today, while avoltage is not applied, LC molecules are parallel to the surfaces ofsubstrates and render "white". On the application of a voltage, themolecules change their director in the direction of an electric field.As a result, sequential transition occurs from the "white" state to a"black" state. However, the viewing angle available with theconventional LCD is limited due to the behavior of the moleculesoccurring in response to the voltage. The limited viewing angle isparticularly noticeable in the rising direction of LC molecules in theevent of halftone display.

Implementations for improving the viewing angle are taught in, e.g.,Japanese Patent Laid-Open Publication Nos. 63-106624 (Prior Art 1hereinafter) and 6-43461 (Prior Art 2 hereinafter). The problem withPrior Art 1 is that it is not practicable without resorting to aphotoresist step and a plurality of rubbing steps not necessary for theproduction of ordinary TN type LCDs. Prior Art 2 needs various kinds ofmicrotreatment including a photoresist step for a common electrode andnot necessary for the production of ordinary TN type LCDs. Further, thetwo substrates must be put together by a highly advanced technology.Moreover, when a voltage is applied to an electrode, it is likely that asufficient electric field does not act in a certain portion, preventingthe LC from sufficiently responding to the applied voltage. This lowerscontrast available with the LCD.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodof producing and driving an LCD easy to produce, excellent in viewingangle characteristic, and high contrast.

In accordance with the present invention, an LCD has two substrates, anLC layer sandwiched between the two substrates and causing a pluralityof regions of different kinds to coexist therein, a first electrodeprovided on at least one of the two electrodes and formed with anaperture, and a second electrode provided on the one electrode inalignment with the aperture.

Also, in accordance with the present invention, an LCD has twosubstrates, an LC layer sandwiched between the two substrates andcausing a plurality of regions of different kinds to coexist therein, afirst electrode provided on at least one of the two substrates, and asecond electrode provided on, but insulated from, the first electrode.

Further, in accordance with the present invention, a method of producingan LCD includes the step of preparing an empty panel having twosubstrates, a first electrode provided on at least one of the twosubstrates and formed with an aperture, and a second electrode providedon the one substrate in alignment with the first electrode. After LC hasbeen injected into the empty panel, the panel is cooled from atemperature higher than the isotropic phase-LC layer transitiontemperature of LC to a temperature lower than the transition temperaturewhile a voltage higher than a voltage to be applied between the firstelectrode and a third electrode facing the first electrode is appliedbetween the second electrode and the third electrode.

Moreover, in accordance with the present invention, a method ofproducing an LCD includes the step of preparing an empty panel havingtwo substrates, a first electrode provided on at least one of the twosubstrates, and a second electrode provided on, but insulated from, thefirst electrode. After LC has been injected into the empty panel, thepanel is cooled from a temperature higher than the isotropic phase-LClayer transition temperature of LC to a temperature lower than thetransition temperature while a voltage higher than a voltage to beapplied between the first electrode and a third electrode facing thefirst electrode is applied between the second electrode and the thirdelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptiontaken with the accompanying drawings in which:

FIG. 1 a view showing rubbing directions particular to a panel includedin a conventional TN type LCD;

FIG. 2 is a section showing another conventional LCD;

FIG. 3 is a section showing an LCD embodying the present invention;

FIG. 4 shows the result of electric field simulation effected with theLCD of the present invention;

FIGS. 5 and 6 show the results of electric field simulation effectedwith comparative examples;

FIG. 7 is an enlarged view showing a specific LC layer included in theLCD of the present invention;

FIG. 8 is a view for describing an LCD which have already proposed; and

FIGS. 9-11 are enlarged views each showing another specific LC layerincluded in the LCD of the present invention.

In the drawings, identical reference numerals denote identicalstructural elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To better understand the present invention, brief reference will be madeto a conventional TN type LCD. While a voltage is not applied to thistype of LCD, LC molecules are parallel to the surfaces of substrates andrender "white". On the application of a voltage, the molecules changetheir director in the direction of an electric field. As a result,sequential transition occurs from the "white" state to a "black" state.However, the viewing angle available with the conventional LCD islimited due to the behavior of the molecules occurring in response tothe voltage.

The implementation for improving the viewing angle and taught in, e.g.,Laid-Open Publication No. 63-106624 mentioned earlier (Prior Art 1hereinafter) will be described with reference to FIG. 1. There are shownin FIG. 1 glass substrates 23 and 33 facing each other. As shown, theglass substrates 23 and 33 each is divided by a microrubbing technologyinto a plurality of areas, i.e., areas I and II each having a particularrubbing direction on a pixel basis. In this condition, LC molecules risein opposite directions and improve the viewing characteristic. Theproblem with Prior Art 1 is that it is not practicable without resortingto a photoresist step and a plurality of rubbing steps not necessary forthe production of ordinary TN type LCDs.

Laid-Open Publication No. 6-43461 also mentioned earlier proposes atechnology for improving the viewing characteristic without resorting tomicrorubbing (Prior Art 2). As shown in FIG. 2, Prior Art 2 includes acommon electrode 32 formed with an aperture or void 34 for generating anon-uniform electric field in the individual pixel. As a result, eachpixel is divided into two or more LC domains, improving the TN viewingcharacteristic. Specifically, when a voltage is applied between theelectrode 32 and an electrode 22 facing it, the aperture 34 generates anon-uniform electric field and thereby causes LC molecules 11 to rise indifferent directions. There are also shown in FIG. 2 alignment layers 21and 31 and substrates 23 and 33.

Prior Art 2 has some problems yet to be solved, as follows. First, PriorArt 2 needs various kinds of microtreatment including a photoresist stepfor the common electrode 32 and not necessary for the production ofordinary TN type LCDs. Second, the two substrates 23 and 33 must be puttogether by a highly advanced technology. Specifically, an ordinary TFT(Thin Film Transistor) or similar active matrix LCD has thin film diodesor similar active elements formed on only one of two glass substratesby, e.g., a photoresist process. The other substrate, generally called acommon electrode, is simply formed with an electrode over its entiresurface. Moreover, because the electrode is absent at the aperture 34,as shown in FIG. 2, it is likely that a sufficient electric field doesnot act on the portion around the aperture 34, preventing the LC fromsufficiently responding to the applied voltage. Particularly, because anordinary LCD renders white while the voltage is not applied, theinsufficient response of the LC prevents black from being clearlyrendered and lowers contrast.

Referring to FIG. 3, an LCD embodying the present invention is shown andincludes two substrates 23 and 33. The substrates 23 and 33 respectivelyhave electrodes 22 and 32 and sandwich a layer of LC molecules 11therebetween. While FIG. 3 additionally shows alignment films 21 and 31for illustrating LC alignment control, the films 21 and 31 do notconstitute any essential part of the present invention. In theillustrative embodiment, the electrode 22 of one substrate 23 is formedwith an aperture 24 and provided with a second electrode 25 aligningwith the aperture 24. A particular voltage is capable of being appliedto each of the two electrodes 22 and 25. In the actual LCD, polarizingfilms are positioned on both sides of the cell, although not shown inFIG. 3. While a voltage is not applied between the electrodes 32 and 22facing each other, the molecules 11 remain parallel to the surfaces ofthe substrates 23 and 33. On the application of a voltage, the molecules11 change their orientation in the direction of an electric field. As aresult, the amount of light transmission of the LCD changes.

The aperture 24 and second electrode 25 aligning with the aperture 24will be described more specifically. In a conventional LCD lacking theaperture 24 and second electrode 25, the direction in which LC moleculesrise is determined by, e.g., a pretilt angle which depends on thealignment film and rubbing direction. In the illustrative embodiment,when, e.g., a voltage higher than a voltage applied between theelectrodes 22 and 32 is applied between the second electrode 25 and theelectrode 32, a non-uniform electric field is generated in the LC layer.As a result, the molecules 11 rise in, e.g., two directions shown inFIG. 3 within the individual pixel. This successfully improves theviewing characteristic of the LCD.

In the embodiment, the electrode or counter 32 is not formed with anyaperture, so the substrate 33 does not need any microtreatment discussedin relation to Prior Art 2. Further, the second electrode 25 can beimplemented as the same layer as a semiconductor constituting TFTs orsimilar matrix elements. this allows the second electrode 25 to beformed only if a mask for a photoresist step is changed. Therefore, theembodiment is practicable without any step added to the conventionalprocedure. Moreover, a voltage is applied even to the second electrode25 in order to insure sufficient contrast. These advantages will bedescribed more specifically with reference to FIGS. 4-6.

FIG. 4 shows the result of electric field simulation effected with asection of the LCD shown in FIG. 3. FIGS. 5 and 6 each shows the resultof particular electric field simulation for comparison. Because theresults shown in FIGS. 4-6 are representative of tonality, neither linesnor numerals for reference are shown for the sake of accuracy oftonality.

In FIG. 4, two horizontal lines at the center respectively correspond tothe upper and lower electrodes 22 and 32 shown in FIG. 3. The electrodes22 and 32 are spaced 5 μm from each other. The second electrode 25 islocated at the center of the lower electrode 22, as viewed in thefigure. The aperture 24 and electrode 25 are sized 6 μm each. For thesimulation, 5 V and 8 V were applied to the electrodes 22 and 25,respectively. In FIG. 4, the regions of the same potential arerepresented by particular tonality.

As FIG. 4 indicates, the second electrode 25 applied with the voltagehigher than the voltage applied to the electrode 22 forms a non-uniformelectric field in the LC layer. The molecules 11 having a positivedielectrically anisotropic characteristic and of ordinary use tend toform an array parallel to the electric lines of force (i.e. verticallines on the equipotential surface). Therefore, the electrode 25 causesthe molecules 11 in the LC layer to rise in the directions shown in FIG.3.

The result of simulation shown in FIG. 5 was obtained with an LCDlacking the aperture 24. For the simulation, 5 V was applied to both theelectrode 22 and second electrode 25. As shown, equipotential linesremain parallel to the surfaces of the substrates. This prevents the LCDfrom achieving the advantages of the embodiment.

FIG. 6 shows the result of simulation effected with an LCD having theaperture 24, but lacking the second electrode 25. This configuration isidentical with Prior Art 2 except for the replacement of the upper andlower substrates. As shown, the LCD implements some degree ofnon-uniform electric field. However, the non-uniform electric field isnot as noticeable as in FIG. 4, failing to sufficiently control therising direction of the LC molecules.

As stated above, the illustrative embodiment achieves not only the sameadvantages as Prior Art 2, but an advantage that it is capable ofcontrolling the rising direction of the LC molecules to a greater degreewith the non-uniform electric field.

In the above embodiment, at least one of two substrates facing eachother with the intermediary of an LC layer is provided with an electrodeformed with an aperture, and a second electrode is aligned with theaperture. It should be noted that the alignment of the second electrodewith the aperture refers to a condition wherein when the LCD is seen ina front view, the aperture and electrode are located substantially atthe same position and superposed on each other. Stated another way, whenthe LCD is seen in a section, the alignment does not mean that theelectrode is located at the same position as the aperture. Therefore,the aperture and electrode may be implemented as a single layer or astwo layers one of which is closer to the front than the other, asdesired.

Assume that the illustrative embodiment is applied to a TFT drive LCD.Then, although the aperture and second electrode may be implemented as alayer independent of TFT layers, it is preferable to implement them asthe same layer as one of the TFT layers in order to prevent the numberof steps from increasing. For example, the second electrode 25 may beimplemented by a chromium layer constituting a gate electrode layer, anda photoresist step is effected at the same time.

The TFT structure with which the embodiment is practicable may be eithera staggered structure or an inverse staggered structure. In addition,the second electrode 25 may be included in any one of the staggeredlayers or may be implemented as an additional layer.

It is not necessary that the aperture 24 and second electrode 25 beprovided with the same size. The aperture 24 may be greater than orsmaller than the second electrode 25, as desired.

In FIG. 3, the molecules 11 are assumed to have a positivedielectrically anisotropic characteristic and the initial alignmentparallel to the substrates 23 and 33. Alternatively, the molecules 11may have a negative dielectrically anisotropic characteristic andhomeotropic alignment perpendicular to the substrates 23 and 33, ifdesired. In addition, the LC material is not limited to the TN typematerial having a twist angle of 90°, but may be replaced with asuper-twisted TN (STN) material or a ferroelectric material.

An alternative embodiment of the present invention will be describedhereinafter. This embodiment is characterized in that an electrode isprovided on at least one of opposite substrates, and in that a secondelectrode is provided on, but insulated from, the electrode. Even withthis configuration, it is possible to achieve the advantages discussedwith reference to FIGS. 3 and 4 and to realize a great viewing angle.

In FIG. 3, the directors of the LC twist in the same direction while themolecules 11 rise in opposite directions in two different areas. We havealready proposed an LCD with a great viewing angle and free fromtonality inversion in Japanese Patent Application No. 7-273614. This LCDuses alignment films not limiting the rising direction of the molecules11 to one direction, and an LC material in which the twisting directionof the director is not limited to one direction. Such an LCD allows fourregions different in the twisting direction of the director and in therising direction of LC molecules to occur automatically within theindividual pixel. Specifically, as shown in FIG. 8, in the LC layer ofour prior proposal, the individual pixel has four regions A, B, C and Ddifferent in the twisting direction of the vector and in the risingdirection of molecules. Because four regions in which the risingdirection of the molecules are sequentially deviated by 90° coexist inthe individual pixel, the LCD achieves a great viewing angle and is freefrom tonality inversion even when seen in the oblique direction.

However, extended researches showed us that because the LCD of our priorapplication stated above causes each pixel to be divided into four kindsof regions at random, and therefore appears rugged when seen from theside. We found that by combining the LCD of the prior application andone of the two embodiments described above, it is possible to implementan LCD having a great viewing angle and free from ruggedness when seenfrom the side. Specifically, by using the non-uniform electric fieldderived from the combination of the electrode having the aperture andthe second electrode aligning with the aperture or from the secondelectrode provided on, but insulated from, the electrode, there can berealized an LCD in which each pixel is accurately divided into fourregions different in the twisting direction of the director and in therising direction of the LC molecules.

In the LCD having the individual pixel divided into four regions, it isdesirable that the second electrode be located on the diagonal lines (inthe diagonal direction) of the individual pixel. For example, and withreference to FIG. 7 the second electrode 25a may be configured in theform of a letter X so as to divide each pixel into four regions alongthe diagonal lines. As a result, an LCD with a great viewing angle isachieved. It is to be noted that the diagonal lines may not be strictlydiagonal, but may be slightly deformed or bent so long as they cansubstantially equally divide one pixel.

Generally, in a color LCD, R (red), G (green) and B (blue) pixels arearranged side by side to constitute a square unit pixel. Specifically,the R, G and B pixels each is not square, but is oblong and has avertical-to-horizontal ratio of 3:1 by way of example. In this case, thecontrol over the rising direction of LC molecules is easy in thehorizontal direction in which the distance is short, but difficult inthe vertical direction in which the distance is long. For example, inFIG. 7, the regions C and D are less stable than the regions A and B;the voltage, cooling rate and other conditions for producing the regionsA, B, C and D evenly are extremely limited.

Another alternative embodiment of the present invention to be describedis capable of quadrisecting the individual pixel stably and easily bybroadening the range of applicable voltages and the range of applicablecooling rates. Briefly, this embodiment is characterized in that thesecond electrode includes a portion parallel to the longer sides of apixel.

Specifically, as shown in any one of FIGS. 9-11, the portions of thesecond electrode 25b, 25c, 25d respectively delimiting the regions C andD are shorter than the corresponding portions shown in FIG. 7. With thisconfiguration, the second electrode allows the regions C and D to beformed more stably and easily and broadens the range of applicablevoltages and that of applicable cooling rates. In any one of FIGS. 9-11,it may appear that the contrast of the LCD is lowered due to the leakageof light through the line along which the regions A and B adjoin.However, in the LCD of the present invention wherein the regionsdifferent in twisting direction are generated in the regions identicalin twisting direction with priority, the region C or D is generated inthe form of a string between the regions A and B. As a result, thecontrast of the LCD is not lowered at all.

Referring again to FIG. 3, how the LCD of the present invention isproduced and driven will be described. In a first embodiment of themethod of producing the LCD and the method of driving it in accordancewith the present invention, a voltage applied to the second electrode 25at the time of drive is higher than a voltage applied to the surroundingelectrode 22, as in the conventional LCD. This provides the molecules 11with a desirable rising characteristic and a desirable viewing angle, asshown in FIG. 3. The voltage to be applied to the second electrode 25may be the same throughout all the pixels or may be different betweenthe pixels (in relation to, e.g., the pixel electrodes). In any case,the rising direction of the molecules 11 can be controlled in the mannershown in FIG. 3.

In the first embodiment, LC is injected into an LC panel. Then, the LCpanel is heated to a temperature higher than the isotropic phase to LClayer transition temperature. Subsequently, the LC panel is cooled to atemperature lower than the above transition temperature. At this coolingstage, (1) a voltage higher than a voltage to be applied between theelectrode with the aperture and the counter electrode facing it isapplied between the second electrode and the counter electrode, or (2) avoltage higher than a voltage to be applied to the electrode on thesubstrate and the counter electrode is applied between the secondelectrode and the counter electrode.

The voltage applied at the cooling stage by either one of the aboveschemes (1) and (2) causes the rising directions of the molecules 11 tobe memorized. Therefore, at the time of driving following the coolingstage, it is not necessary to apply the voltage to the second electrode25, i.e., all that is required is to apply the voltage to the electrode22, as in the conventional LCD.

A second embodiment of the LCD producing method and driving method inaccordance with the present invention is characterized in that tomemorize the rising directions of the molecules 11 during cooling, theLCD contains a small amount of organic polymer. Particularly, it isdesirable to inject LC containing a monomer or an oligomer between thesubstrates, and cause it to react within the LC. The resulting polymerwill be evenly distributed in the LC and will stabilize the risingdirections of the molecules.

To make a polymer out of the monomer or the poligomer by reaction, themonomer or the poligomer may be caused to react (i) in the isotropicphase, (ii) in the LC layer, or (iii) in both the isotropic phase and LClayer. Generally, the above scheme (i) allows the resulting highmolecules to help the regions different in the twisting direction and inthe rising direction exist stably. The scheme (ii) presumably allows thehigh molecules to memorize the alignment direction of LC positively.However, such a difference between the schemes (i) and (ii) is notdefinite. With any one of the schemes (i) and (ii), it is possible toproduce the LCD of this embodiment.

The monomer or the oligomer may be selected from a group of photosettingmonomers, a group of thermosetting monomers, or a group of oligomersthereof. Further, the monomer or the oligomer may contain any othersuitable component.

A group of photosetting monomers or oligomers include not only onesreactive to visible rays but also ultraviolet (UV) setting monomersreactive to ultraviolet rays. The UV setting monomers are particularlydesirable from the easy operation standpoint.

The polymer applicable to this embodiment may have a structure similarto LC molecules containing a liquid crystalline monomer or oligomer.However, a flexible polymer having alkylene chains because the polymeris not always used for the alignment purpose. In addition, use may bemade of any one of monofunctional monomers, bifunctional monomers, andmultifunctional monomers.

The UV setting monomers applicable to this embodiment include2-ethylhexylacrylate, butylethylacrylate, butoxyethylacrylate,2-cyanoethylacrylate, benzilacrylate, cyclohexylacrylate,2-hydroxypropylacrylate, 2-etoxyethylacrylate,NUN-diethylaminoethylacrylate, NUN-dimethylaminoethylacrylate,dicyclopentanylacrylate, dicyclopentenylacrylate, glycydilacrylate,tetrahydrofurfrilacrylate, isobonylacrylate, isodecylacrylate,laurylacrylate, morpholineacrylate, phenoxyethylacrylate,phenoxydiethyleneglycolacrylate, 2,2,2-trifloroethylacrylate,2,2,3,3,3-pentafloropropylacrylate, 2,2,3,3-tetrafloropropylacrylate,2,2,3,4,4,4-hexaflorobutylacrylate, and other monofunctional acrylatecompounds.

Also applicable to this embodiment are monofunctional metacrylatecompounds including 2-ethylhexylmetacrylate, butylethylmetacrylate,butoxyethylmetacrylate, 2-cyanoethylmetacrylate, benzilmetacrylate,cyclohexylmetacylate, 2-hydroxypropylmetacrylate,2-etoxyethylmetacrylate, NUN-diethylaminoethylmetacrylate,NUN-dimethylaminoethylmetacrylate, dicyclopentanylmetacrylate,dicyclopentenylmetacrylate, glycidylmetacrylate,tetrahydrofurfrylmetacrylate, isobonylmetacrylate, isodecylmetacrylate,laurylmetacrylate, morphorinemetacrylate, phenoxyethylmetacrylate,phonoxydiethyleneglycolmetacrylate, 2,2,2-trifloroethylmetacrylate,2,2,3,3-tetrafloropropylmetacrylate, and2,2,3,4,4,4-hexaflorobutylmetacrylate.

Further, there may be used any one of multifunctional acrylate compoundsincluding 4,4'-biphenyldiacrylate, 1,4-bisacryloyloxybenzene,4,4'-bisacryloyloxydiphynylether, 4,4'-bisacryloyloxydiphynylether,3,9-bis[1,1-dimethyl-2-acryloyloxyethyl]-2,4,8,10-tetraspiro[5,5]undecane,α,α'-bis[4-acryloyloxyphenyl]-1,4-diisopropylbenzene,1,4-bisacryloyloxytetraflorobenzene,4,4'-bisacryloyloxyactaflorobiphenyl, diethyleneglycolacrylate,1,4-butandioldiacrylate, 1,3-buthyleneglycoldiacrylate,dicyclopentanyldiacrylate, glyceroldiacrylate, 1,6-hexandioldiacrylate,neopentylglycoldiacrylate, tetraehtyleneglycoldiacrylate,trimethylolpropanetriacrylate, pentaerythritoltetraacrylate,ditrimethylolpropanetetraacrylate, dipentaerythlitolhexaacrylate,dipentaerythritolmonohydroxypentaacrylate,dipentaerythritolmonohydroxypentaacrylate,4,4'-diacryloiloxydimethylstilben, 4,4'-diacryloiloxydiethylstilben,4,4-diacryloiloxypropylstilben, 4,4'-diacryloiloxydibutylstilben,4,4'-diacryloiloxydipentylstilben, 4,4'-diacryloiloxydihexylstilben,4,4'-diacryloiloxydiflorostilben, 4,4'-diacryloiloxydiflorostilben,2,2-3,3-4,4-hexafloropentanediol-1,5-diacrylate,1,1,2,2,3,3-hexafloroproppyl-1,3-diacrylate, and urethane olygomer.

Additionally available are multifunctional metacrylate compoundsincluding diethyleneglycolmetacrylate, 1,4-butanediolmetacrylate,1,3-butyleneglycoldimetacrylate, dicyclopendanyldimetacrylate,glyceroldimetacylate, 1,6-hexandioldimetacryolate,neopentylglycoldimetacrylate, tetraethyleneglycoadimetacrylate,trimethylolpropanetrimetacrylate, pentaerythritoltetrametacrylate,pentaerythritoltrimetacrylate, ditrimethylolpropanetetrametacrylate,dipentaerythritolhexametacrylate,dipentaerythritolmonohydroxypentametacrylate,2,2,3,3,4,4-hexafloropentandiol-1,5-dimetacrylate, andurethanemetacrylate olygomer, and styrene, aminostyrene, and vinylacetate.

Moreover, the drive voltage for driving the elements of this embodimentis effected also by interaction at the interface between the polymericmaterial and the LC material. In light of this, there may be used apolymer containing a fluorine element, e.g., a polymer synthesized froma compound containing 2,2,3,3,4,4-hexafloropendanediol-1,5-diacrylate,1,1,2,2,3,3-hexafloropropyl-1,3-diacrylate, 2,2,2-trifloroethylacrylate,2,2,3,3,3-pendafloropropylacrylate, 2,2,3,3-tetrafloropropylacrylate,2,2,3,4,4,4-hexaflorobutylacrylate, 2,2,2-trifloroethylmetacrylate,2,2,3,3-tetrafloropropylmetacrylate,2,2,3,4,4,4-hexaflorobutylmetacrylate, or urethaneacrylate oligomer.

When the polymer is implemented by a photosetting or UV setting monomer,use is generally made of an initiator for light or UV rays. Theinitiator may be 2,2-diethoxyacetophenone,2-hydroxy-2-methyl-1-phenyl-1-on,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-on,1-(4-dodecylphenyl)-2-hydroxy-2-methylpropane-1-on or similaracetophenone, or benzoinmethylether, benzoinethylether,benzylmethylcetanol or similar benzoin, or benzophenone, benzoyl benzoicacid, 4-phenylbenzophenone, 3,3-dimethyl-4-methoxybenzophenone orsimilar benzophenone, or thioxanthone, 2-chlorthioxanthone,2-methylthioxanthone or similar thioxantone, or any one of diazoniumsalts, sulphonium salts, iodonium salts and selenium salts.

Examples of the present invention and Comparative Examples will bedescribed hereinafter.

EXAMPLE 1

A substrate having an amorphous silicon TFT array was formed on a glasssubstrate by repeating a film forming step and a photolithographic step.The TFT array had 480×640×3 pixels sized 100 μm×300 μm each, and adiagonal display size of 240 mm. In Example 1, the TFT had an inversestaggered structure consisting of a gate-chromium layer, a siliconnitride-insulating layer, an amorphous silicon-semiconductor layer, adrain and source-chromium layer, and a pixel-ITO layer, as named fromthe substrate side. A 5 μm wide diagonal aperture in the form of aletter X is formed in the ITO layer of each pixel electrode, and anelectrode also in the form of a letter X and aligning with the aperturewas formed of chromium. The structure was so designed as to apply avoltage to the electrode independently of a voltage meant for the pixelportion. Because the electrode was implemented by the same layer as thegate electrode, i.e., the chromium layer, no extra steps were needed.

An RGB color filter substrate was used as a substrate facing the abovesubstrate. After the two substrates were rinsed, the alignment films 21and 31, FIG. 3, were applied thereto by spin coating, and then baked at90° C. and 220° C. The alignment films 21 and 31 were implemented by apolyimide alignment material JALS-428 (trade name; available from JapanSynthetic Rubber). Subsequently, the substrates were rubbed by a buffingcloth formed of rayon. Rubbing was effected in the diagonal directionsof the substrates; the rubbing direction of the upper substrate and thatof the lower substrate were different by 90°. Adhesive was applied tothe edge portions of the substrates, and then latex balls having adiameter of 6 μm each were sprayed as a spacer. Thereafter, the twosubstrates were aligned and adhered together under the application of apressure. The adhered substrates were placed in a vacuum tank. After thetank was evacuated, nematic LC ZLI 4792 (trade name) was injected intothe substrate assembly. Two polarizer films were adhered to theresulting LC panel perpendicularly to each other, completing an LCD.

8 V was applied to the X-shaped electrode of the LCD in order to effectdisplay in the conventional manner. A voltage for pixel display wasabout 5.5 V. The LCD was free from tonality inversion in all directionsand achieved a great viewing angle free from ruggedness when seen fromthe side.

The condition of the individual pixel was observed through a microscopeunder the application of the voltage. The observation showed that eachpixel was divided into the four regions A-D, FIG. 7, and that theregions A-D were different in twisting direction and rising directionwhen the substrates were tilted for observation.

Further, the viewing angle characteristic of the LCD during tonalitydisplay was measured at the intervals of 45° in terms of orientationangle. For the measurement, use was made of an LC evaluating deviceLCD-5000 (trade name). It was found that the LCD had substantially thesame viewing angle characteristic in all directions, and did not showany tonality inversion within the angular range of 60°.

Comparative Example 1

An LCD was produced and driven in the same manner as in Example 1 exceptthat a voltage was not applied to the X-shaped electrode. The LCD causedtonality inversion and many after images to occur. Disclination occurredin the individual pixel and sequentially changed from the time justafter the application of a voltage, as observed through a microscope.

EXAMPLE 2

An LCD panel was produced in the same manner as in Example 1 except thata TFT array had a staggered structure. Specifically, a substrate havingan amorphous silicon TFT array was formed on a glass substrate byrepeating a film forming step and a photolithographic step. The TFTarray had 480×640×3 pixels sized 100 μm×300 μm each, and a diagonaldisplay size of 240 mm. In Example 2, the TFT had a staggered structureconsisting of a pixel-ITO (Indium Tin Oxide) layer, a source anddrain-chromium layer, an amorphous silicon-semiconductor layer, asilicon nitride-insulating layer, and a gate-chromium layer.

A 5 μm wide diagonal aperture in the form of a letter X is formed in theITO layer of each pixel electrode, and an electrode also in the form ofa letter X and aligning with the aperture was formed of chromium. Thestructure was so designed as to apply a voltage to the electrodeindependently of a voltage meant for the pixel portion. Because theelectrode was implemented by the same layer as the gate electrode, i.e.,the chromium layer, no extra steps were needed.

An LCD panel was assembled and filled with LC so as to produce an LCD. 8V was applied to the X-shaped electrode of the LCD in order to effectdisplay in the conventional manner. A voltage for pixel display wasabout 5 V. This LCD was also free from tonality inversion in alldirections and achieved a great viewing angle free from ruggedness whenseen from the side.

EXAMPLE 3

A TFT substrate was produced in the same manner as in Example 1 andcombined with a color filter substrate in order to assemble an LCDpanel. The substrates adhered together were placed in a vacuum tank.After the tank was evacuated, an LC solution consisting of nematic LCZLI 4792, 0.2 wt % of UV setting monomer KAYARADPET-30 (trade name;available from Nippon Kayaku) and 5 wt % (with respect to the monomer)of initiator Iluganox 907 (trade name) was injected into the substrateassembly. The resulting panel was heated up to 110° C. and thenilluminated by ultraviolet rays (0.1 mW/cm²) for 30 seconds at 110° C.Subsequently, while a 10 V, 5 Hz sinusoidal voltage and a 5 V, 5 Hzsinusoidal voltage were respectively applied to the X-shaped electrodesand pixels, the panel was cooled at a rate of 20° C./min.

In the above panel, each pixel was successfully divided into fourregions in accordance with the configuration of the X-shaped electrode,as observed through a polarizing microscope. When the cell was tilted,the four regions were found to rise in the directions shown in FIG. 7 onthe basis of a change in brightness.

The voltage to the X-electrode was interrupted in order to effectdisplay in the ordinary condition. The resulting viewing angle was greatand free from tonality inversion even with halftone. The LC rose in fourdifferent regions in accordance with the configuration of the X-shapedelectrode, as observed through a microscope. The viewing anglecharacteristic of the LCD during tonality display was measured at theintervals of 45° in terms of orientation angle. For the measurement, usewas made of the previously mentioned LC evaluating device LCD-5000. Itwas found that the LCD had substantially the same viewing anglecharacteristic in all directions, and did not show any tonalityinversion within the angular range of 60°.

Comparative Example 2

An LCD was produced and driven in the same manner as in Example 2 exceptthat a voltage was not applied to the X-shaped electrode. In the LCD,each pixel was not regularly divided into four regions, causing the LCDto appear rugged when seen in the oblique direction.

EXAMPLE 4

A substrate having an amorphous silicon TFT array was formed on a glasssubstrate by repeating a film forming step and a photolithographic step,as in Example 1. The TFT array had 480×640×3 pixels sized 100 μm×300 μmeach, and a diagonal display size of 240 mm. The aperture was not formedin the ITO of the individual pixel electrode. Further, after theindividual pixel was covered with a nitride film, an X-shaped electrodeof chromium was formed at the center of the pixel. For the othersubstrate, use was made of an RGB color filter. The two substrates wereadhered together in the same manner as in Example 1, and then an LCD wasproduced in the same manner as in Example 1.

A 5 μm wide diagonal aperture in the form of a letter X is formed in theITO layer of each pixel electrode, and an electrode also in the form ofa letter X and aligning with the aperture was formed of chromium. Thestructure was so designed as to apply a voltage to the electrodeindependently of a voltage meant for the pixel portion. Because theelectrode was implemented by the same layer as the gate electrode, i.e.,the chromium layer, no extra steps were needed.

An LCD panel was assembled and filled with LC so as to produce an LCD. 8V was applied to the X-shaped electrode of the LCD in order to effectdisplay in the conventional manner. A voltage for pixel display wasabout 5 V. This LCD was also free from tonality inversion in alldirections and achieved a great viewing angle free from ruggedness whenseen from the side.

In the above panel, each pixel was divided into four regions inaccordance with the configuration of the X-shaped electrode, as observedthrough a polarizing microscope. When the cell was tilted, the fourregions were found to rise in the directions shown in FIG. 7 on thebasis of a change in brightness.

The voltage to the X-electrode was interrupted in order to effectdisplay in the ordinary condition. The resulting viewing angle was greatand free from tonality inversion even with halftone. The LC rose in fourdifferent regions in accordance with the configuration of the X-shapedelectrode, as observed through a microscope. The viewing anglecharacteristic of the LCD during tonality display was measured at theintervals of 45° in terms of orientation angle. For the measurement, usewas made of the previously mentioned LC evaluating device LCD-5000. Itwas found that the LCD had substantially the same viewing anglecharacteristic in all directions, and did not show any tonalityinversion within the angular range of 60°.

EXAMPLE 5

An LC panel was produced in the same manner as in Example 3 except thatthe electrode shown in FIG. 9 was used. The sinusoidal voltage appliedto the second electrode was sequentially varied from 5 V to 20 V whilethe cooling rate of the substrates were sequentially varied from 5°C./min to 20° C./min. In all such conditions, the individual electrodewas successfully quadrisected in accordance with the configuration ofthe electrode. Tonality conversion did not occur in any direction withinthe viewing angle of 60°.

In summary, in accordance with the present invention, an LCD can bedriven with a voltage higher than a voltage applied between an electrodehaving an aperture and a counter electrode to be applied between asecond electrode and the counter electrode. The LCD is free fromtonality inversion and has a great viewing angle over which white doesnot appear during the display of black. Further, the LCD has highcontrast. In addition, the LCD can be produced by a simple procedureneeding no extra steps.

Various modifications will become possible for those skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

What is claimed is:
 1. A liquid crystal display (LCD) comprising:a firstsubstrate with a first electrode thereon, said first electrode having anaperture therein that defines first and second regions of said firstelectrode that are directly adjacent to opposite sides of said aperture;a second substrate with a second electrode thereon, said first electrodefacing and being spaced from said second electrode; a liquid crystal(LC) layer sandwiched between said first and second electrodes, LCmolecules in said LC layer rising when a first voltage is appliedbetween said first and second electrodes; and a third electrode on saidfirst substrate and aligned with said aperture, said third electrodecausing LC molecules in a first portion of said LC layer that isadjacent to said first region to rise in a direction that is differentfrom a rising direction of LC molecules in a second portion of said LClayer that is adjacent to said second region when a second voltagedifferent from the first voltage is applied between said second andthird electrodes and the first voltage is applied between said first andsecond electrodes.
 2. The LCD of claim 1, further comprising a thin filmtransistor having plural electrode layers connected to drive the LCD,said third electrode being independent of said plural electrode layersand on a same level as one of said plural electrode layers.
 3. The LCDof claim 1, wherein said third electrode is entirely within saidaperture on a same level as said first electrode.